When data is recorded in a disk medium, it is also needed to provide management information on locations of the data recorded on the disk medium. Such a management technique is provided by a so-called FAT (File Allocation Table) system, JIS X 0605-1990 widely used for MS-DOS and Windows or a UDF system according to OSTA (Optical Storage Technology Association) Standard adopted for DVDs. These are called as logic standards. The use of any one of the logical standards enables the user to specify the location of any data file on a disk medium by a corresponding file name. As a concept of each directory is defined, it is possible to hierarchically represent storage areas of data on the disk medium. However, the directory is a conceptual frame and, therefore, it cannot directly ensure a physical area on a disk medium.
FIG. 1 is a schematic view representing the relationship between managing information and managed data on a disk according to the MS-DOS system. The FAT file managing system used in the operating system MOS-DOS is such that each directory has a directory entry being a management descriptor for managing files and directories existing in the directory. Each of files and directories is described by 32-byte-information including a file name, a file name extension, a file attribute, a final edit time, a final edit date, a start cluster and a file size.
In case of managing a data file, a start cluster number and a size of a file containing actual data records are recorded. A format in which the data are recorded on a disk can be known by referring to the file allocation table (FAT). In the FAT, for example, each of all clusters on a disk is provided with 16-bit information containing numbers of serially accessible clusters composing a series of files and additional information (0xFFFF) indicting the last cluster. Namely, the management descriptor indicates a number of the start cluster for identifying a beginning position of data recorded on the disk, thereby reading data from the disk can be performed subsequently by referring to subsequent cluster numbers until the marker 0xFFFF appears.
FIG. 2 is schematic view of management information according to a UDF system. Regarding only a portion for managing whereabouts of data files on the disk, the UDF records locations of recorded data in a file entry. The location information is recorded for each unit of serially recorded data. For data recorded as separate blocks on a disk, the location information is managed on block-by-block basis. The management of usage of the disk may be conducted by using a space bit map to be described later with reference to FIG. 3.
A technique for restricting an area for a file on a disk medium is represented by an idea of so-called partition. This technique divides a recording area of a disk into several divisions each of which can be managed individually.
For recording data files on a random-access disk memory, a unit data file 1 such as software or image file can be divided into files 1-1 (File1-1), 1-2 (File1-2) and 1-3 (File1-3) and arranged at different locations as shown in FIG. 4. However, for data needed to be rapidly read from the disk medium within a limited time or frequently read and updated, it is preferable to continuously arrange such data on the disk to reduce the time for seeking and increase a data processing speed. In addition, in a state that data is divided and arranged randomly at different locations on the disk medium, it is difficult to estimate an access time necessary for recording/reproducing actual data on/from the disk medium.
For example, when recording compressed video data on a disk by an encoder MPEG, a way for reproducing data must be considered in advance. Namely, a sequence of video data recorded on a disk in time series must be read, decoded and reproduced in the same sequence of images within a specified duration of time by a decoder MPEG. If the processing should not be completed within the specified duration, the video cannot be reproduced normally for example with dullness or freeze of a scene on the display screen. One of technical means to solve this problem is such that a stream of video data MPEG read from the disk is stored in a buffer memory before decoding the data by the decoder MPEG. The buffer memory may temporarily store therein a certain amount of video data from the disk to prevent being out of synchronism of a servo mechanism due to a shock from outside and breakage in reading video data recorded at different locations due to seeking discrete data elements at different locations. In this case, an allowable time of breakage in reading video data can be determined by the capacity of the buffer memory. However, in such a state that seeks may occur frequently at short intervals, frequently stopping reading video data, it may become difficult to achieve seamless (continuous) reproduction of video data in time series. To increase the allowable time of a short break in reading video data from the disk, it is necessary to store in advance a large amount of video data in the buffer memory, requiring a certain time for reading the data from the disk for which duration no data is output for reproduction. This is a new problem to be solved.
No problem may occur in reproduction of video data if only video data has been recorded serially on a disk from the top thereof. In practice, a disk may contain thereon a variety of data, other than video data, such as a still picture, audio data, management information and programs. On the disk in such state, video data is followed by different type data, for example, a still picture and speech data. In other words, the video data may be discretely arranged on the disk. In reproducing video data discretely arranged on the disk, it is necessary to seek data on the disk frequently, causing short breaks in reading data into the buffer memory. The discrete arrangement of video data on the disk is therefore undesirable.
To avoid this, it is thought to ensure in advance an area for recording video data on the disk so that video data can be recorded continuously therein with no interfere by different type data.
However, to realize the above, it is necessary to previously ensure a certain area exclusively usable for recording video data irrespective of practical usage, for example, even in case of recording no video data.
To preserve an area for exclusively recording video data by using the above-mentioned conventional FAT system, a file allocation table (FAT) corresponding to the reserved area must be set in the used state so that it may not be used by other type data. However, no information is provided which portion of the area is used and which portion of the area is unused. Consequently, it is needed to separately provide an area-usage managing file on the disk. In addition, it is impossible to directly ensure the area on the disk by using a directory since the latter is a mere conceptual framework.
To preserve a certain area for exclusively recording particular data by using the conventional UDF system, it is necessary to manage the ensured area by a file extent function and set a corresponding space bitmap into the use state. In this case, like the case of the FAT system, the area may be reserved so that it may not be occupied by other type data, but its usage cannot be managed since logical level management cannot provide information on which portion of the area is used and which portion of the area is still unused. It is also impossible to directly ensure the area on the disk by using a directory since the latter is a mere conceptual framework.
With FAT and UDF systems, partitions can be defined to restrict respective areas for recording files and directories on a disk but require separate preparation of management information as to usage of each of the partition. In addition, it is impossible to provide a sub-partition within a partition.
FIG. 5 shows a relationship between files and directories arranged on a disk according to a conventional system. As shown in FIG. 5, two directories 1 (DIR1) and 2 (DIR2) are prepared under a root directory (Root), then two files 1 (File1) and 2 (File2) are created under the directory 1 (DIR1) and a file 3 (File3) is created under the directory 2 (DIR2). In the conventional system, the directories are conceptual frameworks for building up a hierarchical structure and, therefore, they cannot ensure actual areas on a disk. Consequently, as shown in FIG. 5 the files 1 (File1), 2 (File2) and 3 (File3) cannot be used as management information limiting respective recording areas on the disk.
The conventional managing method as shown in FIG. 14 can ensure a data recording area on a disk by using a file framework but cannot manage the usage of the file area. It may limit areas for recording files and directories on a disk by defining partitions. This method, however, may increase an amount of management information and complicate the management of file and directories. In addition, this method involves a problem that each partition does not allow further partitioning.